I did a quick search and found this: the first references the Sunpak and the second gices some good advice. I have a B&W for my wide angle and a cheaper maodel for my zoom because they come in more useful in landscape photography (wide-angle).
http://www.photo.net/bboard/q-and-a-...id=0094OD&tag=
and this:
http://www.photo.net/bboard/q-and-a-...Sm&unified_p=1